1. Field of the Invention
The present invention relates to Fourier transform optical apparatus for optically performing image processing or image recognition used by visual recognition systems such as robots.
2. Description of the Related Art
Image processing or image recognition technology in recent years has required processing of a large number of pixels at high speed. Therefore, the optical information apparatus which is capable of high-speed parallel operations has been aggressively developed.
As an example of a prior optical information processing apparatus, the optical information processing apparatus disclosed in Japanese laid-open publication Hei. 2-132412 is described.
FIG. 8 shows the configuration of the prior optical information processing apparatus. In FIG. 8, a reference numeral 20 is a TV camera, 21 is a first liquid crystal display (LCD) that displays an image picked up by TV camera 20, 22 is a semiconductor laser, 23 is a collimating lens that makes parallel rays of the light from the semiconductor laser, and 24 is a first lens. First LCD 21 is set at the front focal plane of first lens 24. 25 is a second LCD and set at the back focal plane of first lens 24.
26 is a read only memory (ROM) that stores the data of Fourier transformed computer generated holograms for the sample point of each pixel on the second LCD for a plurality of reference patterns, that is, the data of impressed voltages corresponding to the transmittance of each pixel on the second LCD 25. 27 is a second lens, and second LCD 25 is arranged at its front focal plane. 28 is a photodetector arranged at the back focal plane of second lens 27.
The operation of the conventional optical information processing apparatus configured as above is described.
First, when TV camera 20 picks up an object, its image is displayed on first LCD 21, while the LCD is irradiated with coherent light emitted from semiconductor laser 22 and collimated by collimating lens 23.
Since first LCD 21 is placed at the front focal plane of first lens 24, a Fourier transform image of the object transformed by first lens 24 is formed on the back focal plane of first lens 24, i.e. on second LCD 25.
At the same time, a Fourier transform image of a particular reference pattern is displayed on second LCD 25 as an optical filter. This image is displayed as a form of Fourier transform computer generated hologram by spatially modulating the transmittance of each pixel of second LCD 25 based on an input signal produced from the data stored in ROM 26. Accordingly, the Fourier transform image of the input object image on first LCD 21 transformed by first lens 24 and the Fourier transform image calculated beforehand from a particular reference pattern are superimposed on second LCD 25.
Further, since second LCD 25 is set at the front focal plane of second lens 27, if the two Fourier transform images of the object and the reference pattern coincide, a luminescent spot is formed on the second focal plane of second lens 27 and detected by photo detector 28.
In this way, optical image processing perform in which an optical filter of a computer generated hologram displayed on second LCD 25 functions as a matched filter.
However, the above configuration has a problem in that the length of the light path becomes long, so that the size of the apparatus becomes large for the following reasons.
Assuming the wavelength of semiconductor laser 22 is .lambda., the pixel pitch of first LCD is P, and the diameter of the Fourier image displayed on second LCD 25 is D, then the focal length f of first lens 24 is given by f=D.times.P/.lambda.. Therefore, if P=50 .mu.m, .lambda.=0.8 .mu.m and D=60 mm, then a lens of f=3125 mm is required. Consequently, the distance between first LCD 21 and second LCD 25 shown in FIG. 8 becomes an exceedingly long 2.times.f=6250 mm.